Which group contains only standard tertiary colours?

Correct answer: Red-orange, yellow-green, blue-violet

The standard tertiary colours are red-orange, yellow-orange, yellow-green, blue-green, blue-violet and red-violet. Option D contains red-orange, yellow-green and blue-violet, all of which belong to that list. The other groups contain primary or secondary colours, or a mixture of categories; therefore option D is the only group made entirely of standard tertiary colours.